At the present time, organic molecular compounds are mainly used for lithium secondary batteries, solar cells and capacitors. From the point of avoiding leakage of an electrolytic solution, technical development is moving toward high molecular weight electrolytes.
Known as such high molecular weight electrolytes are those prepared in combination of a polymer containing an ethylene oxide (EO) unit with an electrolytic salt (metal salt) and those prepared in combination of a polymer containing an ethylene oxide (EO) unit and an electrolytic salt with an organic solvent.
However EO-electrolytic salt-based ion conductors have essential problems such that because a viscosity thereof is high, transfer of dissociated ions is not smooth, and because the electrolytic salt is dissolved in a poly phase crystalline polymer, an ionic conductivity is affected by a phase change, particularly by melting of an EO crystal phase, resulting in a low ionic conductivity at a temperature near room temperature, and further because a crystallization speed is slow, an ionic conductivity changes as time elapses.
Accordingly, in order to decrease a viscosity and also to increase an ionic conductivity at a temperature near room temperature, various trials for enhancing non-crystallinity have been made by changing kind of polyethers. As a result, dependency on temperature is considerably reduced, but actually an ionic conductivity is not so enhanced and is not in a practical level.
As a trial for decreasing a viscosity, it is proposed to introduce bulky CF3 group to EO. For example, JP-A-8-22270 proposes an ion conductor which comprises a fluorine-containing polyether compound comprising a unit of:
and a unit of:OCH2CH2,an alkali metal salt and an organic solvent.
Also JP-A-9-48832 discloses an ion conductor comprising a crosslinked diacrylate containing a fluorine-containing polyether represented by:
where n is from 10 to 20, a metal salt and an organic solvent.
Further JP-A-11-53937 proposes to use a copolymer comprising a fluoroolefin unit and an alkyl vinyl ether or alkyl allyl ether unit having a carbonate bond.
Additionally use of a compound containing a polyfluoroether unit in its trunk chain as an ion conductor is disclosed in JP-A-2003-257240.
However in any of the compounds containing a fluorine-containing ether unit which are disclosed in those Patent Documents, a large ionic conductivity can be obtained only by gelation with an organic solvent because an action of decreasing a viscosity is insufficient.